BEIRUT — Pro-government forces defeated the Islamic State group in its last major stronghold in Syria, state media and a monitoring group reported on Sunday, leaving the militants to defend just strips of desert territory in the country and a besieged pocket outside the capital, Damascus.

Also Sunday, more than two dozen civilians were killed as government forces and rebels traded fire across fronts in Damascus and Homs, Syria’s third largest city.

The intensified violence is testing an accord by Russia, Turkey, and Iran to suppress fighting in Syria ahead of the resumption of political talks in Geneva between the government and opposition, set for Nov. 28.

Eight civilians were killed in rebel shelling on Homs, which also put the city’s al-Walid flour mill out of service, Syria’s SANA news agency reported. It added that another two were killed by shelling or rocket fire on Damascus.

A Syrian boy pushes a bicycle down a street amidst the destruction following reported shelling by Syrian government forces, in the rebel-held town of Douma in Syria’s eastern Ghouta region, on November 17, 2017.Hamza Al-Ajweh / AFP / Getty Images

At least 17 civilians were killed in government shelling and airstrikes on the Eastern Ghouta suburbs of Damascus, which remain under opposition control, according to the Britain-based Syrian Observatory for Human Right monitoring group. The Civil Defence search-and-rescue group, more popularly known as the White Helmets, said one of its volunteers was killed in the line of duty by a rocket.

Residents in the Ghouta region have suffered under an immense government bombardment since rebels tried to storm a military position nearby Tuesday. At least 77 civilians have been killed, according to the Observatory.

The battle with ISIL for Boukamal, on the border with Iraq, featured its share of feints and ruses, with the militants pulling out of the town 10 days ago only to attack it again and threaten to trap pro-government forces inside.

But the militants could not hold it against a coalition of regional forces from Lebanon to Pakistan, organized under Tehran’s leadership to fight the war in Syria. A statement by a shared media outlet for the forces said Iranian Revolutionary Guards Gen. Qasem Soleimani personally directed the operations, and published a video of him posing for photos with fighters celebrating the victory.

Holding Boukamal will be an important strategic objective for the government and its sponsor Iran, which is shifting militias under its authority across both sides of the border.

Units from Lebanon’s militant group Hezbollah, Iraq’s Popular Mobilization Forces militias, Iran’s elite Revolutionary Guards, and the Syrian Army all fought in the battle for Boukamal, according to various statements and interviews with the groups and the Britain-based Syrian Observatory for Human Rights monitoring group, which also reported the militants’ defeat at Boukamal.

This frame grab from video provided Wednesday, Nov 8, 2017 by the government-controlled Syrian Central Military Media, shows a tank firing on militants’ positions on the Iraq-Syria border.Syrian Central Military Media via AP

ISIL has suffered consecutive defeats at the hands of separate but simultaneous offensives in Iraq and Syria by the Russian-backed Syrian forces and allied militias as well as U.S.-backed Iraqi and Syrian fighters.

Despite its recent defeats, the extremist group’s media apparatus has remained active and its fighters are likely to keep up their insurgency from desert areas.